All six episodes from the fourth series of the British crime drama starring Martin Compston, Vicky McClure and Thandie Newton. In this series, AC-12 Superintendent Hastings (Adrian Dunbar) places DS Fleming (McClure) undercover to investigate a possible miscarriage of justice in a murder investigation. Head of the case DCI Roz Huntley (Newton) thinks she's finally found her suspect after months of searching for a serial killer, however, those at AC-12 are led to believe she may be concealing valuable evidence.

As new revelations begin to emerge, will they be able to identify the real perpetrator?